Ability to create groups/tags for compute#151

It would be good to have a feature to create groups of compute instances. This can be then having its own view of billing summaries and total spend per group level as well.

Usecase 1 - A company doing multiple products needs to know the product level expenses.

Usecase 2 - having many clients and a client having multiple instaces can be grouped to gether with better view on billing and usage.